This invention relates to color film, and in particular to film with a random color filter array.
The great majority of color photographs today are taken using chromogenic color film, in which color-forming couplers, which may be incorporated in the film or present in the processing solution, form cyan, magenta and yellow dyes by reaction with oxidized developing agent which is formed where silver halide is developed in an image wise pattern. Such films require a development process which is carefully controlled in respect of time and temperature, which is usually followed by a silver bleaching and a fixing step, and the whole process typically takes several minutes and needs complex equipment.
Color photography by exposing a black-and-white photographic emulsion through a color filter array which is an integral part of the film or plate on which the photographic emulsion is coated, has long been known to offer certain advantages of simplicity or convenience in color photography. Thus the Autochrome process, disclosed by the Lumiere brothers in 1906 (U.S. Pat. No. 822,532) exposed the emulsion through a randomly disposed layer of red, green and blue-colored potato starch grains, and the emulsion was reversal processed to give a positive image of the scene which appeared colored when viewed by light transmitted through the plate. The process allowed the formation of a colored photograph without the chemical complexity of later photographic methods.
The Dufaycolor process (initially the Dioptichrome plate, L.Dufay, 1909) used a regular array of red, green and blue dyed patches and lines printed on a gelatin layer in conjunction with a reversal-processed black-and-white emulsion system which similarly gave a colored image of the scene when viewed by transmitted light.
Polavision (Edwin Land and the Polaroid Corporation, 1977) was a color movie system employing a rapid and convenient reversal processing method on a black-and-white emulsion system coated above an array of red, green and blue stripes, which gave a colored projected image. It was marketed as a still color transparency system called Polachrome in 1983.
These methods suffered a number of disadvantages. The images were best viewed by passing light through the processed film or plate, and the image quality was not sufficient to allow high quality prints to be prepared from them, due to the coarse nature of the Autochrome and Dufaycolor filter arrays, and the coarse nature of the positive silver image in the Polavision and Polacolor systems. The regular array patterns were complicated and expensive to manufacture. In addition, the films which used regular or repeating filter arrays were susceptible to color aliasing when used to photograph scenes with geometrically repeating features.
U.S. Pat. No. 4,971,869 discloses a film with a regular repeating filter array which claims to be less susceptible to aliasing problems. The film comprises a panchromatic photographic emulsion and a repetitive pattern of a unit of adjacent colored cells wherein at least one of the cells is of a subtractive primary color (e.g. yellow, magenta or cyan) or of a pastel color. Scene information can be extracted from the developed film by opto-electronic scanning methods.
EP 935 168 discloses a light sensitive material comprising a transparent support having thereon a silver halide emulsion layer and a randomly arranged color filter layer comprising colored resin particles. The document also discloses exposing, processing and electro-optically scanning the resultant image in such a film and reconstructing the image by digital image processing.
Color photographic films which comprise a color filter array and a single image recording layer or layer pack have the advantage of rapid and convenient photographic processing, as the single image recording layer or layer pack can be processed rapidly without the problem of mismatching different color records if small variations occur in the process. A small change in extent of development for example will affect all color records equally. Exceptionally rapid processing is possible using simple negative black-and-white development, and if suitable developing agents are included in the coating, the photographic response can be remarkably robust or tolerant towards inadvertent variations in processing time or temperature. Developing agents suitable for including in the coating, and a preferred way of incorporating them, are disclosed in U.S. Pat. No. 5,804,359.
It is therefore desired that the color filter array does not impede the transport of processing solutions and processing chemicals through the film, and that it provides a sufficient area of water-permeable material within its structure to enable passage of aqueous solutions through the array as required. This is particularly important if the array is coated further from the film support than the photographic emulsion layer(s), which is a preferred structure for the film.
It is also desirable that the color filter array be manufacturable at comparatively low cost. Known methods of making regular filter arrays, such as those used for Dufaycolor or Polachrome films, are complex and costly, involving several sequential applications of materials to the film. Known methods of making random filter arrays, such as those used for Autochrome film and that described in EP 935 168 also involve complex operations, including separating and grading or sizing the colored particles of starch or resin respectively, dispersing them in a coating medium, coating and drying and then calendaring the coated layer to flatten the particles.
It is an aim of the invention to provide a color filter array film which avoids the problems mentioned above.
According to the present invention there is provided a color film comprising a support layer, at least one light sensitive emulsion layer and a layer formed of a randomly disposed color filter array, wherein the color filter array layer is coated from an aqueous medium and comprises water immiscible colored filter elements which are fluid at the temperatures used in coating and drying.
Preferably the color filter array layer is coated further from the support than the emulsion layer or layers.
The invention further provides a method of forming a color image of a scene from an imagewise exposed photographic film, the film comprising a support layer, at least one light sensitive emulsion layer and a layer formed of a randomly disposed color filter array, wherein the color filter array layer is coated from an aqueous medium and comprises water immiscible colored filter elements which are fluid at the temperatures used in coating and drying, the method comprising developing the image of the scene formed in the emulsion layer, and processing the scanned image information to give an electronically coded representation of the scene.
The film of the invention has the advantage of exceptionally rapid and convenient photographic processing, as it can be processed using simple negative back-and-white development, as opposed to either a reversal process or a chromogenic process. It avoids the disadvantages of aliasing and of high manufacturing cost associated with regular color filter arrays by using a random array which may be prepared simply by coating a layer of suitable colored particles or droplets. The lower image quality formerly associated with random color filter arrays is overcome by means of electronic image processing, which can result in good quality color images, especially in the case of the preferred embodiment having the specified filter element sizes.
Unlike films which employ filter arrays comprising solid particles of resin or starch grains, the film of the invention allows ready access of aqueous processing solutions through the color filter array (CFA) layer. This is desirable because in the case that the CFA is located between the emulsion layers and the support it allows passage of supplementary processing chemicals which may be coated in the film and located between the CFA and the support (for instance, stabilizing, pH modifying or fixing chemicals). In the case that the CFA is located between the emulsion layers and the top coated surface of the film, it allows passage of the processing solutions themselves through into the emulsion layers. Passage of processing solutions through the CFA layer is enabled because of the change of shape of the fluid, water-immiscible colored filter elements which occurs when the CFA layer swells in the processing solution as depicted in FIG. 2.
The color filter array of the invention allows convenient manufacture of films having a preferred film structure in which the CFA is located between the emulsion layers and the top coated surface of the film, that is located further from the support than the emulsion layers. This film structure is preferred because it allows the film to be exposed in the camera with the support towards the back of the camera and the emulsion side toward the lens, which is the orientation for which films and cameras are normally designed. Such a film structure is preferable in the case of Advanced Photographic System films because the magnetic recording layer functions most effectively when coated on the back of the support and has to be in contact with the magnetic heads in the back of the camera. The random filter array preparation methods of the prior art would entail complex operations on top of an already-coated emulsion layer, which would need to be done under safelight conditions and would risk harming the very sensitive coated emulsion layers for instance by causing fog or desensitization. Heat calendaring operations, as used in the method described in EP 935 168 could very probably cause heat and pressure fog in the already-coated emulsion layer(s). Furthermore, the random color filter arrays of the prior art are not expected to allow sufficient permeability to processing solutions, and, because of their more rigid nature, are expected to present problems of adhesion and physical integrity if underlying gelatinous layers were to become soft and swollen, as is required for normal photographic processing.
Reference is made to related commonly owned co-pending applications entitled Method of Making a Random Color Filter Array, U.S. Ser. No. 09/808,844, and Random Color Filter Array, U.S. Ser. No. 09/810,787, now U.S. Pat. No. 6,326,108 both filed concurrently herewith, the entire contents of which are incorporated herein.